Bubbles under rowing boat

[James HS]

Everyone says this is the nirvana.

what is happening when you get 'bubbles' under your boat and does it indicate the amazing oarsmanship that most people think?

Thanks

James

[carl]

It normally indicates that air is being entrained into the water flowing
under & against the hull.

1. For this to happen requires an air/water mixing process which must
require significant local turbulence & therefore absorb some energy, but
asking how much energy it requires is like asking the length of an
arbitrary piece of string.

2. If enough air enters the boundary layer, that should reduce the drag
due the shear within the boundary layer (that narrow layer of water
between the hull and the undisturbed main stream), but by how much is
again unquantifiable.

3. Any air/water mixing must generate local turbulence, which is likely
to advance the normal transition from laminar to turbulent flow within
the boundary layer. Since that transition brings increased drag per
unit area of hull, initiating it sooner would be disadvantageous unless
the gains from #2 exceed the losses from 1 & 3.

But it is an invigorating sound, so maybe you'll go faster & finish a
little more fatigued?

Cheers -
Carl

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